1. Field of the Invention
The present invention relates to a knocking control device for a turbocharged internal combustion engine.
2. Description of the Prior Art
Usually, in a turbocharged internal combustion engine, the objects being to increase the engine output and specific fuel consumption, an increase of the intake air pressure due to the turbocharger results in an increase in the temperature of the intake air. In order to increase the charging pressure at a low engine speed and to enlarge the turbocharging effect, the sectional area of the nozzle from which the exhaust gas flows into the turbine must be as small as possible. As a result, the exhaust gas pressure increases at a high engine speed and knocking easily occurs. Particularly, continuous, heavy knocking results in a decrease in the engine output and in the durability of the engine. Ultimately, it results in the destruction of the engine. Therefore, although by decreasing the compression ratio of the engine knocking is less frequent, increasing the engine output and specific fuel consumption in an engine with a turbocharger is to no avail.
In the prior art, knocking is detected and the ignition timing is delayed in accordance with the knocking. As a result, the decrease in the engine output and in specific fuel consumption is minimized. However, in this delay control of the ignition timing, since knocking is avoided, the temperature of the exhaust gas becomes extremely high, the parts of the exhaust system are exposed to a high-temperature atmosphere, the durability of the parts is decreased, the temperature of the residual gas in the cylinders of the engine rises, and knocking easily occurs. The aim of the present invention is to solve the above-mentioned problems.